1. Field of the Invention
This invention relates to radial run-flat pneumatic tires and, more particularly, to a run-flat tire having a structural helical coil compression element inserted in the inside of the casing of the tire and to a method of making the same.
An area of tire technology which has engaged investigators over the years is the run-flat pneumatic tire concept. A run-flat pneumatic tire is one designed to support a vehicle for operation even if the tire has partially or totally lost its inflation pressure. The advantages of such a tire in safety, convenience, cost, and weight and space saving are obvious. A recent successful development in the art of run-flat tires is the band-reinforced radial tire invented by one of the inventors in the present application, which banded tire is the subject of U.S. Pat. No. 4,111,249, granted to Edward G. Markow and assigned to the assignee of the present invention. The run-flat tire in that Markow patent, U.S. Pat. No. 4,111,249, is hereby incorporated herein by reference.
A banded run-flat tire is a pneumatic radial tire having a casing with a crown and sidewalls extending from the crown on either side to annular beads which, in a conventional way, are used to mount the tire in a sealed relationship on the rim of a wheel. In the design, the band element, which usually is a thin structural ring of high-strength steel of a fiber/epoxy composite, is incorporated circumferentially into the crown of the tire under the tread thereof. Radial tires, as is well known, have one or more plies containing a multiplicity of closely spaced radial reinforcing cords or wires in the sidwalls of the tire casing. In the tire disclosed in the above referenced patent to Markow, the radial cords or wires function as spoke-like reinforcing elements to stabilize the circumferential band. When the tire is deflated, the radial spoke-like elements and the band stabilized thereby form a load-sustaining structure analogous to an elastic arch. In the design, the band receives vertical, drag, and side loads from the road or ground surface, and carries those loads in compression and bending; the radial spoke-like elements act as tension members to support the axle. A prime function, also, of the closely spaced radial elements is to stabilize the thin band against buckling.
Currently suggested banded tire designs under serious consideration usually call for a band embedded in the crown of the tire underlying the tread. Thus, during the manufacture of the tire, it is required with such designs that the band be integrated into the "green" carcass or casing. During the cure cycle, there has to be an accommodation for transient molding pressures that may degrade the structural integrity of the band. Of course, when the band is embedded in the crown itself of the tire, the retrofitting of existing radial tires with a band to derive the advantages thereof becomes economically infeasible.
2. Description of the Prior Art
There is a showing in the prior art by V. Alfredo Roque (U.S. Pat. No. 3,734,157) of a vehicle tire having annular wire or rod strengthening elements contained in a plurality of separate ridges on the inner surface of the tire casing. Lacking radial spoke-like reinforcing wire or cord elements in the tire sidewalls cooperating with an annular band, V. Alfredo Roque does not disclose a true radial run-flat tire, however, the teaching therein of annular reinforcing elements in the inside surface of the crown of the tire is of interest. Because the annular elements are strengthened by annular rods or wire clusters, they have a fairly high degree of rigidity. Thus, they have to be incorporated into the tire during the construction thereof prior to the forming of the beads. This consideration applies also to the annular bands taught in the banded radial run-flat tire disclosed in the previously referenced U.S. Pat. No. 4,111,249 to Markow.